High molecular weight linear polyesters and copolyesters of glycols and terephthalic or isophthalic acid have been available for a number of years. These are described inter alia in Whinfield et al, U.S. Pat. No. 2,465,319 and in Pengilly, U.S. Pat. No. 3,047,539, incorporated herein by reference. These patents disclose that the polyesters are particularly advantageous as film and fiber formers.
With the development of molecular weight control, the use of nucleating agents and two-step molding cycles, poly (ethylene terephthalate) has become an important constituent of injection moldable compositions. Poly(1,4-butylene terephthalate), because of its very rapid crystallization from the melt, is uniquely useful as a component in such compositions. Workpieces molded from such polyester resins, alone or combined with reinforcements, in comparison with other thermoplastics, offer a high degree of surface hardness and abrasion resistance, high gloss, and lower surface friction.
Stable polyblends of poly(1,4-butylene terephthalate) and poly(ethylene terephthalate) can be molded into useful unreinforced and reinforced articles. See Fox and Wambach, U.S. Pat. No. 3,953,394, incorporated herein by reference.
Block copolyesters containing units derived from poly(1,4-butylene terephthalate) and from an aromatic/aliphatic or aliphatic polyesters are also known. See, copending application U.S. Ser. No. 752,325, filed Dec. 20, 1976, incorporated herein by reference. Such block copolyesters are useful per se as molding resins and also in intimate combination with poly(1,4-butylene terephthalate) and/or poly(ethylene terephthalate).
It has been proposed to increase the impact strengths of polyesters by adding various modifiers. For example, Brinkmann et al in U.S. Pat. No. 3,591,659 disclose that a useful family of modifiers comprises polyalkyl acrylates, methacrylates and/or ethacrylates. Barron et al in U.S. Pat. No. 4,044,073 disclose that a useful impact modifier for such polyesters is an aromatic polycarbonate. Schlichting et al in U.S. Pat. No. 4,022,748 disclose that a rubber-elastic graft copolymer having a glass temperature below -20.degree. C. is a useful modifier. Lane, U.S. Pat. No. 4,034,013, and Farnham et al, U.S. Pat. No. 4,096,202 disclose that useful impact modifiers comprise multiple stage polymers having a rubbery first stage and a hard final stage, preferably including units derived from alkyl acrylates, especially butyl acrylates. Baron et al in U.S. Pat. No. 4,034,016 (corres. German Pat. No. 2650870) disclose an impact modifier combination comprising a blend of a polyurethane and an aromatic polycarbonate. Copending application Ser. No. 957,801, filed Nov. 6, 1978, now Pat. No. 4,257,937, discloses an impact modifier combination comprising a poly(alkyl acrylate) and an aromatic polycarbonate. Gergen et al., U.S. Pat. No. 4,090,996 disclose an impact modifier combination comprising a vinyl aromatic-diene copolymer in combination with a "dissimilar engineering thermoplastic." All of the foregoing patents and the application are incorporated herein by reference. Filled reinforced and/or flame retardant modifications of such polyesters are also well known in the art.
It has now been discovered that such polyesters can be greatly improved in impact strength by intimately admixing therewith an impact improving modifier combination comprising a polyacrylate resin or a vinyl aromatic-diene copolymer and a poly(1,3-butylene terephthalate)resin. The latter is not an engineering thermoplastic in the sense used in the above-mentioned Gergen et al. patent.
As will also be shown, the new compositions of this invention can be reinforced, filled, reinforced and filled, and all modifications can be rendered flame-retardant.